Indicator



July25, 1944. F. R. 51A; 2,354,618

INDICATOR Filed Nov. 9, 1942 entor: Y Frederick R Sias,

His Attorney.

Patented July 25,1944

INDICATOR Frederick R. Bias, Marblehead, Masa, aasignor to General Electric New York Company, a corporation of Application November 0, 1942, Serial No. 485,081

3 Claims.' (CI. I'll-)5) My invention relates to telemetering systems and concerns particularly arrangements for electricallytransmitting mechanical motions, either of rotation or deflection.

It is an object of my invention to provide a sturdy, reliable, compact receiver or indicator for remote indicating or telemetering systems.

- It is an object of my invention to provide a telemeter receiver or electrical ratio indicator in which the angular length of the scale may be adjusted and in which the angular positions of the scale ends may be adjusted independently of each other. The telemetering system as such described in this application is claimed in a divisionlsl application Serial No. 499,542, filed August 21, 43.

' A further object of my invention is to provide a telemetering system of the type having a variable resistance or potentiometer with a sliding brush .to serve as a transmitter, and to provide a receiver for such a system, in which there is no danger of false scale indication in the case of a break in brush connections or bad contact.

It is also an object of my invention to provide such a system and a receiver therefor in which a change in the transmitter resistance has relatively little effect on the calibration curve of the receiver, in which a given transmitter may be used with a brush movement, representing transmitter scale length, varying from approximately 90 degrees to 240 degrees-without serious departure from straight line calibration of the receiver, and in which the operation and the torque char acteristics of the,receiver may readily be predicted by graphical solution.

A further object of the invention is to elimicoil is connected between the ungrounded terminal of the current source and ground in series with a resistor, the resistance of whichis adiustable for adjusting the angle of the scale of the receiver.

In the preferred form of construction the receiver coils are mounted on an aluminum form which serves as a damping cylinder interposed between the coils and the rotor. The rotor is preferably a right circular cylinder composed of high coercive force material such as sintered 'oxide described in Patent No. 2,248,818, Faus. The aluminum form or damping cylinder and the coils are surrounded by a hollow cylinder composed of permeable magnetic material to serve as a magnetic shield. Within the cylindrical space defined by the shield a short pull-oil magnet, composed of high coercive force material, is mounted with its magnetic axis eccentric with respect to the rotor but transverse to the axis of rotation thereof, and the pull-off magnet is made sufilciently powerful to deflect the rotor to an oilscale position when no current is supplied to the electrical coils, which may happen in case of a power failure. If desired, the scale may be 80 arranged that the pointeris obscured when the-- rotor is in the off-scale position in case of power failure, but I prefer to have the pointer visible atalltimes.

A betterunderstanding of the invention will be afforded by the following detailed description nate. the danger of false indications in case of 4 power failure.

Other and further objects and advantages will become apparent as the description proceeds.

In carrying out my invention in its preferred form I provide a receiver or indicator having a pair of current-conducting coils mounted at an angle to each other in inductive relation to a rotor and electrically connected to a transmitter, comprising a resistor having a pair of adjustable taps for varying the transmitter scale length and having a sliding brush or tap which is moved along the resistor in accordance with variations,

in the indications .to be transmitted. One of the taps is connected to a current source at its line terminal and the other is grounded, the current source having a grounded terminal. One of the receiver coils is electrically connected between the first tap and the sliding brush. The other considered in connection with the accompanying drawing, and the features which I consider to be novel and patentable will be pointed out in the claims appended hereto.

In the drawing Fig. l is a top view of one'embodiment of my invention; Fig. 2 is, a sectional view of the arrangement of Fig. 1 representing a section cut by a broken vertical plane 2-2; Fig. 3 is an exploded perspective view of the apparatus of Figs. 1 and 2; Fi 4 is a circuit diagram of a telemetering system embodying my invention in which a receiver or indicator may be employed of the type represented in Figs. 1, 2

and 3; Fig. 5 is a circuit diagram of a telemeter nology implying a vertical rotor axis is for convenience only and is intended to include a receiver mounted in any position.

In Figs. 1 to 3 the illustrated receiver or indicator comprises a base H composed of suitable insulating material such as fibrous material impregnated with a phenolic condensation product, a combined winding form and damping cup [2 composed of an electrically conducting material such as aluminum, for example, a hollow cylindrical magnetic shield i3 surrounding the damping cup i2 with a space therebetween, a pair of coils l4 and i5 mounted at an angle to each other, with radial magnetic axes, in the space between the damping cup l2 and the magnetic shield l3, s. top bridge 56, which may be composed of magnetically permeable material closing the top of the magnetic shield l3, and a rotor l'l mounted within the damping cup I! having an axis of rotation substantially concentric with the damping cup and the magnetic shield. 11 the top bridge i8 is composed of material which is magnetically permeable in order to provide magnetic shielding additional to that provided by the cylindrical shield IS, a magnetic shield plate (not shown) may also be mounted at the bottom of the shield I3 or under the damping cup it against the base ii. Good results are obtained by making the angle between the coils H and I! about 140", but this angle may be varied to obtain different angular scale lengths. The rotor H is a permanent magnet which is preferably composed of a high coercive force material having a definite line of polarization which is not readily changed in any direction such as described in the aforesaid Faus patent. Preferably the rotor ll consists of a cylinder which is transversely magnetized carried by a spindle l8 having suitable pivots or journals l9 and 20 at the ends cooperating with suitable bearings.

The lower bearing may consist of a conventional jewel screwii screwed into the base of the clamping cup 12, held in adjustment by a lock nut 22 and carrying a cup jewel 23 at the upper end thereof cooperating with the rotor pivot 26. The upper bearing may consist of a bridge bushing 24 composed of a non-magnetic material such as brass or bronze, for example, pressed into a center opening in the top bridge l6 and having a contracted throat portion 25 (Fig. 2) serving as a ring bearing to cooperate with the upper Journal.

An indicating pointer 2! may be mounted at the upper end of the Journal is to cooperate with a. graduated arcuate scale 21. For enabling indications of power failure to be observed when the pointer 28 is deflected to off-scale position, ample space is provided at the lower end 28 of the scale, which is the region of the scale occupied by the pointer when it is deflected below the zero position.

The damping cup ii is preferably arranged in spool shape having a flanged base 2!, which is solid except for a threaded opening to receive the Jewel screw 2|, and having an upper flange 30, whereby the hollow cylindrical magnetic shield l3 may be fitted over the damping cup I! in engagement with the flanged portions 28 and 30, leaving a space ll for the'coils l4 and II. For supporting these coils preferably projections 32 and 33 are formed in the damping cup it. It will be understood that suitable openings are provided in the damping cup 11 for electrical cone ductors leading to the coils H and I. For example, a pair of insulating bushings N and II (Fig. 3) may be mounted in openings in the lower flange 2| registering with corresponding openings (not shown) in the insulating base H which has channels (not shown) connecting with cavities for terminals 36 and 31. Likewise a pair of insulating bushings is mounted on the other side in the lower flange 2! for carrying leads to a second pair of terminals 38 and II.

In order to maintain the magnetic shield ll in a predetermined angular position and thus guard against possible changes of calibration in the event of lack of perfect concentrioity of mounting and uniformity of construction of the magnetic shield, a notch 40 is provided in the lower end of the magnetic shield. A projecting lug H is iormed at one side of the flanged base 28 of the damping cup I! to register with the notch M. Notches u may also be provided in the upper flange ill to register with tapped holes 43 in the top bridge Ii. The tapped holes I are adapted to receive scale-supporting screws (not shown).

The top bridge I6 is secured to the damping cup I! in any suitable manner as by means of screws 45 to hold the magnetic shield IS in place. The shield II in turn holds the coils II and II in place on the projections 32 and 33. The ma!- netic shield it may be composed of any suitable high permeability magnetic material such as that known as Mu-metal, for example.

The coils and I! consist of flat wire-wound spools formed by cementing acetate films 4| and 41 (Fig. 3) to annular cores ll (Fig.2) to form fiat spools on to which wire 4! is wound to form a flat coil, which is thereafter hot molded under pressure in the curved form shown in Fig. 3. It

desired krait paper insulation I. (Fig. 2) may be provided between the damping cup and the coils I4 and ii on the one hand and the ni -I- netic shield I! on the other hand.

It will be observed from the drawing that the bridge bushing 14 is held in place in the opening in the top bridge 2| by fitting the bushing into the top bridge and in effect peening over the upper edge ll of the shoulder on the bridge bushin 24.

is shown the bushing 14 has a downwardly extending enlarged portion I! in the shape of a square with the corners beveled. A pull-oi! field tor pulling the pointer oil-scale in case 0! power failure is provided by means of a short permanent magnet II occupying a transverse hole cut in the square portion 2 oi the bushina 24. The magnet I3 is composed of material which has a relatively high coercive iorce and a relatively low operating permeability (not initial permeability). The high coercive force assures adequate magnetic held for the intended p se in spite oi the short length of the magnet and the low permeability guards against the rotor II inducing flux in the magnet It taking up an anguin position degrees from that which it is intended to have under the action of the pull-oi! magnet is when the current supply in the coil: 14 and ll is cut oil. Thus the permanent msgnet tleld oi the magnet 8 acts with the permanent magnet held of the rotor magnet 11, but the rotor l'l does not produce any appreciable induced polarization of the magnet rod II which might cause the rotor l1 to take up a position 180 degrees from that which it would tend to take up by reason of the permanent magnet field of the magnet II. v

assesia Pull-oil magnets composed of 86 per cent cobalt steel, relatively long, and mounted relatively far from the rotor to avoid strong induced magnetizatlon have been used in instruments not having a small magnetic shield. When a magnetic shield is employed the pull-off magnet must be inside the shield. In the case of a compact instrument with a small shield, particularly,- the pull-off magnet is brought very close to the permanent magnet rotor and must be very short. The resuit is that, even in the case of the usual highcoercive force permanent magnet alloys, the

magnetic pole strength induced in the pull-off magnet by the field of the permanent-magnet rotor becomes large in comparison with the magnetic pole strength of the pull-of! magnet due to c I 3 or to the polarity of terminals specified. A Junetion vterminal I of the coils l4 and il is connected to a sliding brush adapted to move adjustable by means of movable taps 02 and' I8.

its own permanent magnetism. For proper oper- I ation of the instrument, however, the permanent magnet flux of the pull oil magnet should be substantially greater than that induced in it by the rotor. Consequently, I utilize a special material for the pull-off magnet 53.. I have successfully used a low permeability permanent magnet material such as an alloy of approximately 50 per cent copper, per cent nickel, and per 25 cent iron or a similar alloy in which 2% per cent cobalt replaces so much iron, heat treated to give high coercive force as described in-Patent No. 2,196,824, Dahl. Thirty-six per cent cobalt steel has a coercive force of approximately 210 oersteds, a residual magnetization of 9,600 gausses and a maximum permeability of 35. In contrast, the aforesaid copper nickeI-iron-cObaIt alloy has a coercive force of 290 and a residual magnetization of 7350. I do not know its maximum per- 86 meability but assume that it is of the same order of magnitude as that of the aforesaid coppernickel-iron alloy which. has a maximum permeability of approximately eight and values of parable with those of the heat-treated alloy including 2 per cent cobalt.

With the proportions of parts and spacings shown in the drawing and using either of the As the brush '0 is caused to slide along the re sistor I, it varies the relative voltages applied to the coils It and i5 and therefore the relative currents, so that the rotor ll takes up a position depending upon the relative magnitudes of the fluxes produced by the currents flowing in the ,coils I4 and II. Accordingly, the pointer 28 deflects to a position indicative of the position of the brush 60. In case a break should occur in the conductor ll between the coil junction terminal l8 and the sliding brush ",the coils i4.

and i! will carry the same current and the rotor would take up a fixed position which under ordinary circumstances is the mid scale position regardless of the position of the brush 00. The

length of the scale angle of the indicator, that is, the angular distance from the 'zero point II to the full scale point 00 (Fig. 3) is determined by the angles between the coil holding projections 32 and II on the damping cup l2. The preferred angle is about 140 degrees. Different angles may be provided by utilizing diflerent damping cups for instruments intended to have different lengths of scale, or by shifting the position of the I I locating hole in coils M and II. coercive force and residual magnetization compreferred heat-treated alloys which I have men- 4 tioned for the pull-off magnet 58, the flux induced in the pull-oflf magnet by the rotor is about one quarter of the flux due to the permanent magnetization of the pull-off magnet.

The damping cup I: has formed integral thereof very compact light-weight high-torque units.

My invention is not limited to indicators of a particular size and rating. However. it may be mentioned that telemetric indicators giving very satisfactory performance and having a torque as high as four or flve hundred milligram-centiso meters may be constructed with a shield diameter of no greater than flve-eighths inch and a rotor diameter no greater than five-sixteenths inch in a construction such as illustrated in the drawing.

If the indicator of Figs. 1 to 3 is utilized in a telemetering system of the type represented by Fig. 5, the coils I4 and II are connected as shown in series between the positive terminal I1 and the negative or grounded terminal of a source .of current with a current-limiting protective resistor 51, preferably connected in the positive lead. This is the conventional connection, but

I The modifled arrangement of Fig. 6 may be employed in which an open circuit in the brush connection or a poor contact between the brush II and the resistor ll causes current failure'and thus allows the rotor H to take up a position determined by the angular position of the pull-oi! magnet 08 in which position the pointer 20 is moved of! scale and thus no false indication is produced. It will be observed that in the arrangement of Fig.6 thejunction terminal I of the coils i4 and I5 is connected to the positive side 51 of the current source and the brush .0 is grounded so that the coils l4 and 48 form branch circuits. Thus when the brush III is at one end of the scale, for example, adjacent the transmitter scale end adjustment tap If, one of the coils, in this case the coil I4, is connected directly across the current source 51, ll whereas the other current coil I5 is connected in series with the transmitter resistor 8i. It stands to reason that the angular position of the pointer under these circumstances at either end of the scale, in this case the zero end, depends upon the resistance of the portion of the resistor ll between the tape 02 and N.

5 Apparatus of this kind is frequently used in connection with float gauges for tanks in which the brush is is connected through a linkage .1 to a float II which rises and falls according to the level of liquid in a tank I. Since the angular movement of the brush produced by floats acting in different tanks varies, the taps '2 and N are made adjustable so that they may be moved opposite the points at which the brush ll rests when the float is at the empty and full my invention is not limited to grounded systems 7 tank positions respectively. For example, the

- the tap t2.

the calibration and scale length of the indicator depend upon the physical arrangement of the tank with which the float gauge telemetering system is used. 'The variation in scale length of T the indicator may be reduced by continuing the resistor ll around the full circle by providing a portion ti as shown in dotted lines in Fig. 8.

The scale length of the receiver or indicator may be made independent of variations in the transmitter resistance by employing the arrangement illustrated in Fig. 4. In this case a transmitter resistor ll is again employed having a sliding brush El and taps I: and 3, adjustable to provide for different limits of travel of the transmitter-actuating mechanism such as the float orlinkage 01-". The resistor 51' in the positive lead to the current source terminal I! is provided and the indicator coil I4 is connected in series with the sliding brush is and the positive lead through the resistor ll. The transmitter scale adiustment tap 82 is also connected in series with the resistor 51' to the positive source terminal ll. Thus the coil It forms a circuit between points I! and I! on the resistor \I. The second coil II is connected in a circuit between the positive and negative terminals 81 and It of the current source. For adjustment of the angular length of the receiver scale ll a resistor t8. the resistance of which may be varied, is connected in-serles with the coil ii. Movement of the brush I along the resistor II will produce variations in the voltage drop in the coil l4 and therefore cause variations in the flux strengths of the coils i4 and II, causing deflection of the rotor il in accordance with movement of the brush II. The end position of the receiver pointer 28 at the zero-end of the scale is determined solely by the angular position of the current-conducting coil II, for when the brush II is at the position of the tap 82 no current flows in the coil i4. Preferably, the scale is marked so this end-scale position is a little to the left of the zero mark, so that the pointer standsat zero when the brush II is a little to the right of A break in the connection to the brush it or a poor contact cannot cause any false indication of a partially filled tank. for example, because in this case the rotor will take up the position determined by the coil ll, viz: a position below the zero position. In the case of a complete power failure or a break in the current-- source connections ll, ll, also the pointer 2. will be deflected below the zero position to the scale end II by the pull-off magnet ll.

. Adjustment of the length of the scale 21 of the l indicator may be made by varying the resistance of the resistor 06 because the rotor position is determined by the relationship between currents inthe coils l4 and II when the brush is at the transmitter position of the tap 03. Preferably the full-scale mark is a little to the left of the point corresponding to the position of the tap ll.

' current inthe coil il doesnot depend upon the resistance of the resistor I and therefore the length of scale of the indicator is independent of any variations in its transmitter resistance.

and with proper transmitter resistance as deter mined by the constants of the coils I4 and II of resistor It and by pull-off magnet strength becomes astraight line within about one degree.

Such a result is obtained, for example. with a 120 degree scale angle, when the constants, stated by way of illustration and not by way of limitation, are as follows:

Resistance between taps 62 and 0!---ohms-.. 400 Resistance of resistor I do 400 Resistance of coils l4 and I5, each do 205 Pull-off torque equalling one-eighth the averaae coil torque. Average coil torque -gram mm 4 The scale linearity may also be affected by the varrangei'nent of the shield l8 if it has any eccentricity. or if it is not perfectly circular. The shield eilect is explained more in detail in my copending application, Serial No. 472,317, filed January 14, 1943. The scale may be compressed at either end or made substantially linear, by variation in the constants. However, a two to one change in transmitter resistance has comparatively little eilect. Accordingly, with the average value chosen for a linear calibration, the angular spread between the tape '2 and I! may be changed over wide limits, viz: from about to 240 degrees to take care of different brush movements produced by floats in different tanks without serious departure from straight line calibration of the indicator. Furthermore, since the current in, each of the coils l4 and ll is independent of the current in the other coil the operation of the apparatus and the torque characteristics of the indicator may readily be predicted by graphical methods.

- I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its practice and showing its application, but it will be obvious to those skilled in the art that many modifications and variations are possible, and I aim therefore to cover all such modifications and variations as fall within the scope of my invention which are defined in the appended claims:

What I claim as new anddesire to secure by Letters Patent of the United States is:

1. An indicator comprising a damping cup composed of electrically conducting material, a hollow shield composed of magnetic permeable material surrounding the cup and spaced therefrom, electrically conducting coils with radial magnetic axes fitted between the damping cup and the magnetic shield, a rotor rotatably mounted within the damvihs cup. and electrical connections to the coils whereby variations in the relative current strengths in the coils produce variations in the resultant direction of the magnetic field produced by the coils and thereby produce a deiiection of the rotor, the rotor comprising a magnet magnetlsed in a direction transverse to its axis of rotation.

2. An indicator such as described in claim 1 having a relatively short bar magnet moimted within the space defined by the magnetic shield for biasing the magnetic rotor to a predetermined gluon in case of failure of current supplied to coils.

7| 3.Anindicatorsuchasdescribedinclaim1 having a relatively short bar magnet mounted within the space defined by the magnetic shield and transverse to the axis of rotation 01 the rotor for biasing the magnetic rotor to a predetermined position in case of failure of current supply to the coils, said bar magnet being composed ot a material having a coercive force substantially as high as that characteristic of an alloy of 50 per cent copper, 20 per cent nickel, and 30 per cent iron, with a permeability substantially as low as that 5 characteristic of such an alloy.

FREDERICK R. SIAS. 

